Self-healing “artificial leaf” produces energy from dirty water

The "artificial leaf" created by Daniel G. Nocera, Ph.D. and his team now has self-healing capabilities (Photo: Dominick Reuter)

Back in 2011, scientists reported the creation of the “world’s first practical artificial leaf” that mimics the ability of real leaves to produce energy from sunlight and water. Touted as a potentially inexpensive source of electricity for those in developing countries and remote areas, the leaf’s creators have now given it a capability that would be especially beneficial in such environments – the ability to self heal and therefore produce energy from dirty water.

While the leaf mimics a real leaf’s ability to produce energy from sunlight and water, it doesn’t mimic the method real leaves rely on, namely photosynthesis. Instead, as described by Daniel G. Nocera, Ph.D. who led the research team, the artificial leaf is actually a simple wafer of silicon coated in a catalyst that, when dropped into a jar of water and exposed to sunlight, breaks down water into its hydrogen and oxygen components. These gases can be collected as they bubble up through the water to be used for fuel to produce electricity in fuel cells.

Because bacteria can build up on the leaf’s surface and stop the energy production process, previous versions of the device required pure water. Now Nocera’s team has found that some of the catalysts developed for the artificial leaf actually heal themselves, meaning the process can work with dirty water.

“Self-healing enables the artificial leaf to run on the impure, bacteria-contaminated water found in nature,” Nocera said. “We figured out a way to tweak the conditions so that part of the catalyst falls apart, denying bacteria the smooth surface needed to form a biofilm. Then the catalyst can heal and re-assemble.”

Where similar devices are expensive to manufacture due to the use of rare and expensive metals and complex wiring, Nocera’s artificial leaf uses cheaper materials and a simple “buried junction” design that he says would make it cheaper to mass produce. Additionally, less than one liter (0.25 gal) of water is enough to produce around 100 watts of electricity 24 hours a day. And while it isn’t necessarily the most efficient form of electricity generation, Nocera likens the approach to “fast-food energy.”

“We’re interested in making lots of inexpensive units that may not be the most efficient, but that get the job done. It’s kind of like going from huge mainframe computers to a personal laptop. This is personalized energy.

“A lot of people are designing complicated, expensive energy-producing devices, and it is difficult to see them being adopted on a large scale,” he added. “Ours is simple, less expensive, and it works.”

Nocera believes the artificial leaf is likely to find its first use in individual homes in areas that lack traditional electric production and distribution systems. As well as being cheaper than solar panels, because the artificial leaf doesn’t directly generate electricity, but produces hydrogen and oxygen that can be stored, the electricity could be generated for use at night.

The research team hopes to integrate the artificial leaf with technology for converting the hydrogen into a liquid fuel to power everything from traditional portable electric generators to cars.

Nocera described the artificial leaf at the 245th National Meeting & Exposition of the American Chemical Society that is currently being held in New Orleans.